showing posts tagged "distortion"
18 Mar 2019
tags:  bowed  plucked  distortion  bow-response  theory  

A Violin is not a Guitar

An Electric Violin is not a Funny Shaped Electric Guitar

Am I stating the obvious? Apparently not since most electric violins are built and used a lot like an electric guitar.

What's the difference?

Bowed vs Plucked.

We all know the difference between bowed and plucked. But surprisingly few people have thought through the difference in instrument design that stems from this initial difference.

This is really simplified, but I'm going somewhere with it so bear with me.

A plucked string gets energy imparted to it once per note at the start. It starts off with a sideways movement in the direction of the pluck but quickly settles to a more circular movement as it dies away. How quickly it dies away depends on the mobility of the bridge and soundboard to which it is attached. The less mobile the bridge is, the more sustain but the less volume, as the vibration is reflected back into the string. The more mobile it is, the louder but less sustain as the energy is sucked faster into the body and soundboard. It's a direct tradeoff - this is why a banjo is loud with little sustain - it has a highly mobile bridge because it is mounted on a skin. It is also why electric guitars have more sustain than acoustic guitars - the bridge is mounted rigidly on several kilos of solid wood! Electrics overcome the lack of volume with an amp (obviously). You can make an electric guitar with less sustain by making a more mobile bridge, but since the sustain is musically useful in many situations most electric guitars don't do that.

A bowed string has energy imparted continuously. There is no tradeoff between sustain and volume because the sustain is created by adding more energy rather than by trying to conserve the energy already in the string. In fact making a bowed instrument with a less mobile bridge creating more sustain actually makes it harder to play and control because the energy reflected back into the string causes the string to want to keep resonating by itself, rather than being controlled by the bow.

To complicate matters the stiffness of the bridge will vary with pitch. Most existing electric violins that use a bridge based on a acoustic bridge will have a somewhat mobile bridge at high frequencies since most of the mobility at those frequencies is in the bridge itself - however the bridge is still very stiff at the fundamental frequency of the string(s) since it is attached to a rigid body, and most of the mobility on an acoustic at fundamental frequencies is in the belly, bassbar and air resonance of the instrument, none of which exist on a typical electric violin.

Since it is mostly the fundamental frequency of the note that determines the bow feel on the string the mobility at high frequencies doesn't help much.

The Violorama violin has the exact same action of top, soundpost and bass bar as an acoustic - the only thing missing is the air resonance - if it had that it would BE an acoustic which would defeat the purpose - however the air resonance is substituted for by the resonance of the bass bar assembly which is much more complex than an acoustic bass bar.

Another important difference between plucked and bowed instruments is the direction of the vibration in the string. A plucked instrument sustain quickly settles to an approximately symmetrical movement that moves about the same amount either side of the resting point.

On a bowed string the vibration is offset to one side, because the bow is dragging the string to one side. Furthermore, the direction of the offset changes every time the player changes bow direction. This has consequences for pickups and amplification since the electronics must accommodate the maximum movement to each side even though that is larger than half the peak to trough displacement of the waveform at any time - so we need electronics with greater headroom if we want to ever have a clean sound.

A related issue is that the raw waveform of the string is very different on a bowed string. A plucked string has an initial burst of complexity and harmonics and then settles to a fairly simple tone with fewer harmonics at a lower level. A bowed string is constantly being pushed out of its natural resonance and the waveform has a very different shape, at root rather like a sawtooth wave as the string is dragged sideways by the bow then snaps back suddenly, then does it again. This wave is also fairly simple when considered as a wave - but contains a much higher proportion of harmonics than a guitar wave. Using this bright waveform picked up directly off the bridge as most electric violins do is part of what creates the characteristic mosquito-like tone of many electric violins.

However, even if the wave is allowed to develop into a warmer version of itself though the mobility and resonances and frequency dependent damping of the instrument then the fundamental difference in the harmonic content of the sound needs to be considered at every stage, from designing the preamp through to choosing effects and amps.

Because a bowed string is primarily moving from side to side the violin family has evolved a lever action to convert this to the in-an-out movement of the top that is best for transmitting sound to the air. On an electric we no longer care about transmitting sound to the air - in fact we are trying to prevent it. However the lever action is so essential to the natural movement of a violin that keeping it is necessary to make the electric feel and sound like a violin. Keeping this element of acoustic design in an electric violin also affords us many possibilities for influencing the tone of the instrument, and some locations to have pickups where they can sense a more gracious tone than that directly from the bridge.

Effects in Context

The signature sound of an electric guitar is overdrive / distortion. This is remarkably well suited to the electric guitar since it adds harmonic content to the relatively simple natural tone of the plucked string, and also increases sustain even further. You could even say that it improves the guitar by making it sound more like a violin! Of course that's only partly true, as distortion harmonics have a quite different spectrum profile to the natural violin harmonics.

When you take a violin with a sound that is already bright and harmonically full and add overdrive distortion you get harmonics on the harmonics of the original tone - the sound can quickly become over-complex and unmanageable. This might be useful depending on your style of music. Noise music and music where the primary parameter is texture will find it more useful than it is for music where harmony and melody are primary. It won't easily give you a euphonious melodic lead sound like an electric guitar though.

There's a few things you can do about this:

One is to filter the violin sound down to a simpler tone before adding distortion. Then you shift the tone from noisy overcomplexity to something more like an electric guitar lead tone. However it is difficult to filter the violin tone without also losing articulation and expression. This may or may not matter depending on the style. If you do this filtering with fixed EQ it will only work well in one register and have to be adjusted for a different register.

You can also split the signal and layer distorted tone with clean, or just use less distortion. Or any combination of the above.

The other approach is to abandon the distortion envy and concentrate on effects that work with the existing plentiful harmonics in the violin tone, rather than adding new ones. Wah, phasing, and many sorts of effects based on resonant filters seem very well suited to electric violin. They have so much more to work with than on electric guitar. (Unless the electric guitar has distortion applied first.)

Delay, reverb and other time-based effects are also more audible and effective if the tone they are applied to is clear and articulate - something that is hard to maintain with distortion on electric violin.